1. Field of the Invention
The present invention relates to three-dimensional thick fabrics, and more particularly to fabrics made from a laminate of different fabric plies made of yarns extending generally in two mutually perpendicular directions which is secured together by yarns extending through the thickness of the fabric in a third direction different from the first two directions.
2. History of the Prior Art
Three-dimensional thick fabrics are presently used in a variety of applications including such things as heat shields in aerospace applications. In the case of heat shields and other ablative components, the end component is preferably made from a thick fabric of carbonizable or carbon-containing yarns interwoven to form a three-dimensional fabric and thereafter impregnated with a thermosetting resin which is then cured and carbonized as desired to form a carbon-carbon composite.
To provide for structural integrity and other desired properites three-dimensional thick fabrics of the type used in ablative applications are preferably formed using three different yarn systems which extend in different directions and which are interwoven with one another. The three different yarn systems can be interwoven simultaneously on a flat loom or using a circular loom. Where a flat loom is used the yarns are interwoven to form a flat fabric which is then opened into the desired circular configuration. Disadvantages of such fabrics may include the inability to weave certain shapes or configurations in the flat and non-uniformities in the density or thickness of the resulting circular fabric including seam lines in many cases. An alternative is to weave the fabric in circular form such as by use of a circular loom. In such arrangements a first yarn system extends along the length of the circular fabric so as to be interwoven with a second yarn system extending generally circumferentially around the fabric with a third yarn system extending through the thickness of the fabric walls so as to be interwoven with both the first and second yarn systems. Such circular loom arrangements are capable of weaving seamless circular fabrics of relatively uniform density. However, the procedure is relatively slow and expensive.
Because of the disadvantages in weaving threedimensional thick fabrics in the flat or using a circular loom, considerations such as cost frequently dictate that the fabrics be made from a laminate of plies of two-dimensional fabric held together by a third yarn system or its equivalent. It is known, for example, to wrap a tape in which yarns extend longitudinally and transversely or alternatively at a bias angle around a mandrel or other form to a desired thickness. It is also known to cut patterns of fabric from preimpregnated material and to stack the patterns of fabric in interleaved fashion and at an angle around a form. In a still further prior art technique a multi-ply laminate is formed, following which holes are drilled through the thickness of the laminate with rods being inserted in the hole to maintain the integrity of the laminate. This technique involves certain disadvantages including some reduction in the strength of the resulting laminate due to removal of portions of the yarns as the holes are drilled through the laminate. It is also known to stitch a laminate of plies of fabric or other material together. Various techniques therefor and needles and other apparatus used in connection therewith are shown by U.S. Pat. Nos. 461,793 of Briggs, 3,649,428 of Hughes, 3,224,399 of Lightner et al, 3,468,274 of Koffler, 437,083 of Bennett, 3,222,891 of Wignall, 2,274,468 of Bell, 4,144,612 of Yamaguchi, Re. 18,954 of Fox, 2,982,242 of Wolf and 4,154,061 of Umemoto et al. Many generalized techniques including some of the various techniques shown in the above patents have not been successfully employed in making three-dimensional thick fabrics of the type suited for ablative and similar applications. This is due to a number of factors including the difficulty in applying techniques of the type shown in the art designed for use with different types of materials to the carbonizable yarns and weaving techniques typically used in conjunction therewith to make three-dimensional thick fabrics for ablative and similar applications.
Further problems arise in the manufacture of three-dimensional thick fabrics which are of hollow, circular configuration and which have a varying diameter. Heat shields, for example, may assume complex shapes which include ogive shapes, conical sections and cylinders, sometimes all in the same part. Such shapes are extremely difficult if not impossible to weave in the flat and are difficult to make and therefore extremely costly using a circular loom.
Accordingly, it is an object of the invention to provide improved three-dimensional thick fabrics and methods and apparatus for making the same.
It is a further object of the invention to provide an improved method and apparatus for securing a laminate of fabric plies together using a third yarn system to form a three-dimensional thick fabric.
It is a still further object of the invention to provide improved three-dimensional thick fabrics of hollow circular configuration and methods and apparatus for making the same.
It is a still further object of the invention to provide improved three-dimensional thick fabrics of hollow, circular configuration and of varying diameter, and methods and apparatus for making the same.